Bad miss on mag check then smooths out.

Roger Lee wrote:

How big an rpm drop? Plugs are usually bad or good and not intermittent. If it's a bad or severe miss it isn't a single bad  plug. Usually a bad plug, plug cap or wire is around 300 ish rpm drop

The miss shakes the engine real bad at 4000, one cylinder is not firing with one mag off.

Thinking out loud, I can reduce the problem to (4) plugs/wires/cap by which ignition system it is. Then reduce that to one side of the engine with EGT temp change. That will get me down to two possibilities.